Re-examination of Thermogravimetric Kinetic Analysis of Lignite Char Gasification

Abstract

Kinetic analysis of CO2 gasification by thermogravimetry was examined employing chars from a Victorian lignite. The gasification of char from the rigorously acid-washed lignite was extremely slow. More than 600 min was required for the complete gasification as a result of a near absence of inherent alkali and alkaline earth metallic (AAEM) species. It was nonetheless necessary to strictly choose the following conditions for eliminating the mass transfer effect: an initial mass of char of <1.3 mg, a particle size of char of <125 μm, and a total gas flow rate of ≥1000 mL standard temperature and pressure min–1. Such requirement arose from the inhibition of non-catalytic gasification by CO within the char particle. On the other hand, the char from the original lignite was gasified much faster than the non-catalytic gasification and completed within 50 min by catalysis of the inherent AAEM species. The measured rate of catalytic gasification was, unexpectedly, independent of the initial char mass and particle size and gas flow rate. This was reasonably explained by no or little importance of CO inhibition in the catalytic gasification. This study has also drawn another important conclusion that the non-catalytic gasification obeyed first-order kinetics with respect to the char mass. The rate constant was steady over the entire range of char conversion, while both the specific surface area and carbon-type distribution of the char varied along with the conversion.

Change in Catalytic Activity of Potassium during CO2 Gasification of Char

“…The present authors initially expected that k cat ′ was steady or near-steady over the entire range of X , following previously reported relationship between d X /d t versus X for the gasification of a Victorian lignite that had inherent metallic species (Na; 0.08, K; 0.01, and Ca; 0.06 wt %) and SiO 2 /Al 2 O 3 (ca. 0.5 wt %). , However, under the present conditions, k cat ′ increased significantly with X . The dependency of k cat ′ on m cat,0 ′ at X > 0.4 was also unexpected.…”

“…0.5 wt %). 36,49 However, under the present conditions, k cat ′ increased significantly with X. The dependency of k cat ′ on m cat,0 ′ at X > 0.4 was also unexpected.…”

“…They analyzed the relationships between the specific reactivity, (d X /d t )/(1 – X ), and the Na concentration in gasifying char for different initial Na concentrations and suggested that loss of intrinsic reactivity of char caused the decrease in the specific reactivity under the catalysis. On the other hand, a recent study on the CO 2 gasification of lignite char, in which was free from metallic species, showed that the first-order rate constant (i.e., k nc ) was steady over the entire range of char conversion …”

“…The other char sample, K-0.16-0.8-A-Si, was prepared by physically mixing K-0.16-0.8-A with SiO 2 nanoparticles at a mass ratio of 0.1, as mentioned in Section . This sample was prepared for intentionally causing the deactivation of residual (acid-insoluble) K prior to and during the gasification. , …”

Virtual Special Issue of 7th Sino-Australian Symposium on Advanced Coal and Biomass Utilisation Technologies

“…Sun et al (10.1021/acs.energyfuels.9b02682) explore the effect of char–tar–H 2 O interactions on gas–liquid–solid products during biomass–steam gasification. Asano et al (10.1021/acs.energyfuels.9b02946) examine the kinetics of the non-catalytic and catalytic gasification during CO 2 gasification of chars from a Victorian lignite. He et al (10.1021/acs.energyfuels.9b02992) explore the effect of Ca and phorsphorus (P) on the interactions between quartz (as bed material) and wood doped with potassium (K) salts under both steam gasification and combustion atmospheres.…”